I have the following structure of my (test) docs

So multiple subfolders with branch index files, and 2 final leaf branches (Resume and doks).
The menu is automatically generated up to the Hugo branch, but is showing the Themes branch as a link:

If I click on it, it shows the Leaf branches as child pages, but the menu is completly missing.

This is the content of the themes/_index.md

---
title: "Themes"
description: ""
lead: ""
date: 2023-01-08T18:36:57+01:00
lastmod: 2023-01-08T18:36:57+01:00
draft: false
images: []
menu:
  docs:
    parent: "hugo"
    identifier: "themes-d2a0fff51bd74ae05d1ca74d383e0959"
weight: 999
toc: true
---

Is this happening because there is some limit on the sublevels? Can this be modified?